5Scanning Probe Microscopy of Nanoclusters
Lifeng Chi and Christian R?thig
5.1Introduction
The invention of the scanning tunneling microscopy (STM)[1]presents the begin-ning of a novel class of near-field microscopy with nanometer till atomic resolution in real space.Originally the STM was designed for the surface analysis under ultrahigh vacuum (UHV)conditions on conducting surfaces.It was verified soon that this method could also be used under a variety of environmental conditions such as ambi-ent air [2],water [3],oil [4]and electrolytes [5].These exciting discoveries motivated the further development of a whole family of other scanning probe microscopes (SPM)[6].Examples include scanning force microscopy (SFM)(or atomic force mi-croscopy ,AFM)[7]and its extensions [8]and scanning near-field optical microscopy (SNOM)[9].
The applications of SPM increased rapidly in the last decade.Since the requirement of a conductive surface for STM is not the necessary condition for SFM,the objects for SPM are extended to insulating materials and cover a wide range of surfaces of bulk systems such as metals [10],semiconductors [11],adsorbates on solid surfaces [12],polymers [13],biological materials [14]and organic layered systems [15].Besides the fundamental research of surface structure,surface morphology and surface recon-struction,the SPM can also be used to reveal local physical properties of the sample,e.g.electronic energy spectra by using local tunneling spectroscopy (LTS,or scanning tunneling spectroscopy ,STS),local tribological properties by using frictional force mi-croscopy (FFM),local elasticity by using force modulation microscopy (FMM),local magnetic properties by using magnetic force microscopy (MFM),and local electro-static properties by using electric force microscopy (EFM).Another important approach of SPM techniques is in the field of nano-lithography [16].
In recent years,nanometer-sized clusters of metals and semiconductors have received increasing scientific and technological interest [17].Introducing chemically synthesized or physically evaporated nanoclusters on a variety of surfaces is a recent approach to generate nanostructured surfaces,which are promising for novel sensoric,electronic and photonic devices and are therefore inducing increased research activ-ities.The SPM,especially STM and SFM,can yield valuable information on nanoclus-ters as they may reveal the electronic and geometric structure of the cluster's.Further more,they can serve as ideal tools to characterize cluster covered surfaces since a wide range of materials can be chosen as substrates for cluster deposition.
In the following,we will discuss the fundamental principle of SPM (Section 5.2)and different operating modes used experimentally (Section 5.3).In Section 5.4,se-lected applications of SPM on nanoclusters will be presented,including:l imaging of individual nanoclusters and cluster covered surfaces l local physical properties
l SPM-based local deposition and modification l tunneling spectra of nanoclusters
Characterization of Nanophase Materials .Edited by Zhong Lin Wang
Copyright 2000Wiley-VCH Verlag GmbH
ISBNs:3-527-29837-1(Hardcover);3-527-60009-4(Electronic)
134Chi
Besides the typical nanocrystalline materials prepared with gas-phase synthesis, and organic ligand stabilized monocrystalline clusters,systems described here will also include the nano-scale metallic dots or islands generated by STM/SFM tips,by nano-sphere lithography and by electroless deposition.The limitation of SPM methods to study the nanophase materials and the prospects will be given in Section5.5.
5.2Fundamental of the techniques
The basic idea of scanning probe microscopy(SPM)is relatively simple:take a probe susceptible to the property one wants to measure,bring it into the vicinity of a surface and measure the reactions of the probe.As one is interested in microscopic information the probe has to be sufficiently small and its movements have to be con-trolled on a length scale comparable to its size.By taking measurements at different locations close to the surface,for instance by scanning the probe at constant height,a topographic representation of the surface can be gained.Depending on the specific property measured,the type of probe and the way in which the reaction of the probe is amplified,all existing SPM methods can be differentiated.
The probe in SPM is usually connected to or consists of the very end of a rigid tip. The movements of this tip relative to the surface are controlled by a scanner con-structed from piezoceramics in most setups which scans either the tip or the surface. The distance between tip and surface is controlled by a similar transducer,quite often all three transducers are combined in a singular unit providing movement in all three spatial directions.If one is only interested in recording a special surface property as a function of the spatial coordinates it is sufficient to amplify and record the reactions of the probe in a proper way.If the interest is on constant-property-maps or if the property changes very drastically with slight changes in tip-sample distance,a feed-back circuitry of some kind is necessary.With it the interesting property is held con-stant and the distance is changed until the set-point is reached.By recording the dis-tance as a function of the two other spatial dimensions a surface plot can be produced. Obviously such a scheme is relatively easy to implement if the interesting property is a monotonous function of the distance(interatomic forces being a prominent example of a more complicate case).Figure5-1shows a typical setup for SPM schematically. The oldest SPM method which lead to resolutions comparable to the best electron microscopes was scanning tunneling microscopy(STM).With it the local electronic density of the surface is measured by applying a small voltage between the probe and surface.The probe is usually formed by the foremost atom of a thinned rigid piece of wire and is connected via a sensitive amperemeter to the surface.If the probe approaches the surface,tunneling of electrons between surface and tip can be ob-served.This tunneling current I is a function of easily controllable independent pa-rameters like the coordinates of the probe relative to the surface and the applied volt-age and dependent parameters like the work function of the surface or the electric conductivity.The general form of the tunneling current is given by
I=I(x,y,z,U)(5-1)
Even from very basic quantum mechanical calculations,i.e.one-dimensional tun-neling through a rectangular barrier,it is evident that the tunneling current exhibits an exponential dependence from the distance between tip and surface.One finds[18]:
I G U r s (0,E F )e
±1.025
F W
p (5-2)
local density of states of the sample:
r s (z,E )=1e P E E n E àe
j y n z j
2
(5-3)
where:
U tunneling voltage F work function
W distance between tip and sample
Typical values for the work function are in the range of 4to 5eV which leads to typ-ical decay constants of about 10times per ,i.e.the tunneling current is reduced by an order of magnitude if the distance between tip and sample is increased by only 1 .Scanning force microscopy (SFM)does not record surface properties directly like STM but measures the forces that are caused by the interaction between probe and surface.These minute forces are recorded by measuring the bending of a small canti-lever to which the probe is connected and which compensates the forces acting on the probe.The movements of the cantilever are therefore a very good representation of the tip-surface interaction.One finds that for ratio of the displacement of the cantile-ver and the piezo [18]:
D z c D z p
1
k
F H d
à1(5-4)
with D z being the displacement of the cantilever and piezo,respectively,k the
spring constant and F ￠(d )the force gradient,a function of the distance d between probe and sample.
Scanning Probe Microscopy of Nanoclusters
135
Figure 5-1.Schematic SPM setup.The solid lines represent a setup with feedback circuitry,the dotted lines a setup without.
Another local probe method uses the optical properties of the surface:scanning near-field optical microscopy (SNOM).In contrast to the optical far-field which is being used in common microscopes the optical near-field is capable to carry information about objects with lateral dimensions much smaller than the wavelength of light used.To exploit this approach the probe has to be susceptible to light intensity,so usually tips made from glass fibers or small apertures are used.If one probes the optical near-field intensity in this way one does not only get distance information by measuring the inten-sity,but one can also measure the spectra of the emitted light to get additional informa-tion about the chemical composition or other optical properties of the surface.
5.3Experimental approaches and data interpretation
In this section,we will focus on different operation modes of scanning tunneling mi-croscopy ,scanning force microscopy and scanning near-field microscopy .We will not describe all the modes but only those included in this chapter for the characterization of nanoclusters.
5.3.1Scanning tunneling microscopy (STM)/Scanning tunneling spectro-scopy (STS)
For scanning tunneling microscopy ,a number of measurement modes have been developed which represent special surfaces of the function I =I (x,y,z,U ):
I =I (x,y,)|U,z =const.
(5-5)
136
Chi
Constant Height Mode (CHM)
I =I (x,y,z )|U =const.=const.
(5-6)
Constant Current Mode (CCM),z being the feedback parameter
I =I (U )|x,y,z =const.
(5-7)
(Scanning)Tunneling Spectroscopy and
I =I (z )|x,y,U =const.
(5-8)
(Scanning)Tunneling Spectroscopy
One can deduce from Eq.5-2that the first spectroscopy mode I =I (U )will yield information about the local density of states r S while I =I (z )will provide information about the local barrier height.By scanning the tip over the surface at a constant cur-rent I a surface of constant local density of states of the sample at the location of the tip is imaged according to this simple model.The assumptions of this model are valid if small tunneling voltages are used and an arbitrarily fast method is employed to cor-rect the distance W .
For larger tunneling voltages,especially for the interpretation of STS measure-ments,more sophisticated models have to be employed.One of these approaches is the first order perturbation approach by Bardeen [19],later refined by Tersoff and Hamann [20,21].If k B T is much smaller than the feature sizes in the energy spectrum of interest one can show that
I =4p e
h R eU
0r s E F àeU e r T E F e j M j 2
d e (5-9)M mn =à h 2
2m R S (F *n
?Y m ±Y m ?F *n )d S (5-10)
with r s and r T being the density of states of sample and tip,respectively,and Y m and F n their wave functions.The tunneling matrix element M mn has the dimension of energy and describes the lowering of energy due to the overlap of the two states m and n .It is important to note that the expression is symmetric,i.e.exchanging tip and sam-ple does not change I .That means for practical purposes that there is no easy way to decide whether the tip has measured the surface structure or the surface has measured the tip structure (for instance via a sharp protrusion).The resulting image will always represent a convolution of tip and surface structure.
Apart from the topographic structure and position on a given surface the electronic structure is of major interest as well from the viewpoint of basic understanding of clus-ters as from a technological point of view.For basic understanding clusters are expected to exhibit a number of electronic properties which position them right in the middle between molecules and the solid state.If we consider the mode of tunneling spectroscopy with respect to the measurement of the gap resistance one would expect to measure the distinct electronic energy levels present in a small cluster system right below the Fermi level.In fact we will see that these attempts have been made in the past,a thorough interpretation of the obtained data,however,is extremely difficult due to the vicinity of the substrate's electronic system and temperature effects.More
Scanning Probe Microscopy of Nanoclusters
137
138Chi
obvious is the charging effect in insulated clusters,i.e.clusters which have a ligand-shell or which are insulated by some other kind of layer from the underlying substrate. Provided these clusters are located not to far away from the conducting surface,tun-neling from the tip to the cluster and from the cluster to the surface will take place.If the tunneling frequency from the cluster to the surface is sufficiently low electrons tunneling from the tip to the cluster will experience the electric field from the excess electrons in the cluster resulting in a quantised tunneling behavior which becomes visible as distinct steps in the I/U-curves.
The second spectroscopic mode,i.e.the measurement of I(z)to determine the work function,is very interesting from a basic point of view.Small free sodium clus-ters for instance show a very strong dependence of their ionization potential from the number of atoms present in the cluster[22,23].However,data interpretation of this kind of spectroscopy,i.e.the determination of work function as a function of cluster size,is quite difficult as the observed clusters will usually not be free but more or less strongly attached to a surface and the number of atoms such clusters consist of can only be determined from a measurement of the cluster volume which in itself is sub-ject to severe uncertainties due to the folding between cluster and tip structure.
5.3.2Scanning force microscopy(SFM)
Scanning force microscopy senses the overall forces between the probe and the sample surface,where the probe is attached to a cantilever-type spring.The images are related to the total density of(valence-)electron states up to the Fermi level at the surface.It is therefore independent of the electrical conductivity of the sample. The force exerted on the tip deforms the cantilever elastically.Since the spring con-stant c of the cantilever is known,the net force F can be derived directly from the deflection D z according to the equation F=c D z.Measurement of the deflection of the cantilever is a main issue in performing SFM.
Different methods were used at the beginning stage of instrument development [24].Now most of the commercial instruments use the laser beam deflection tech-nique proposed first by Meyer et al[25]and Alexander et al[26].A laser beam is reflected from the backside of the cantilever.The deflection is monitored with a posi-tion-sensitive detector(PSD).This signal is used to drive the feedback loop.The experimental setup is schematically shown in Fig.5-3.Depending on the motion of the cantilever,SFM can be divided into static SFM and dynamic SFM.The typical
Figure5-3.Schematic illustration of the
scanning force microscope using the laser
beam deflection method for measuring
the cantilever bend and the torsion due to
the forces between the tip and the sample
surface.
Scanning Probe Microscopy of Nanoclusters139 interaction force between the tip and the sample is between10±6to10±12N,depending on the spring constant of the cantilever and the environmental medium.Most of the commercially available SFM tips are made of microfabricated silicon nitride(Si3N4) or silicon with a tip radius of2±10nm.
5.3.2.1Contact mode SFM
Contact SFM runs in quasistatic mode.The probing tip is brought into a static mechanical contact with the sample.In analogy to the constant current and constant height mode of STM,the common contact mode SFM operates in constant force mode or constant height mode.In constant force mode,the force is controlled by keep-ing the deflection of the cantilever constant by means of the feedback loop.The out-put of the feedback yields the motion of the z piezo thus maps the surface contour.In the constant height mode the feedback loop is not used and the deflection of the canti-lever is measured.In this way higher scan rates can be achieved which minimizes the thermal drift effects.
Detecting the torsion mode of the cantilever instead of the bending mode during scanning allows the study of lateral(friction)forces with the SFM.By using a quad-rant PSD,the normal and the lateral(frictional)force can be monitored simulta-neously[27].The development of friction force microscopy(FFM)allows the study of local tribological properties of samples.
5.3.2.2Dynamic mode SFM
A significant increase in possibilities of the force microscopes was achieved by the use of dynamic modes.Dynamic modes are usually more sensitive leading to less (damaging)interactions between probe and surface and they provide information about dynamic properties such as energy dissipation or local elasticity.
In dynamic SFM the cantilever is driven to vibrate near its resonant frequency by means of a)a piezoelectric element,or b)an external force.Instead of measuring the quasi-static cantilever deflections,changes in the resonant frequency as a result of tip-sample interaction are detected.This a.c.-detection method is sensitive to the force gradient rather than to the force itself.Two different methods are commonly used to measure the frequency shift.One is to measure the amplitude changes or the phase shift of the cantilever vibration with the deflection sensor and a lock-in amplifier[28]. The feedback loop adjusts the tip-sample separation by keeping the force gradient constant.The other one is to measure the change in oscillation frequency with a fre-quency counter or a frequency modulation(FM)discriminator.The feedback loop is adjusted to keep the frequency constant.Some physical properties such as magnetic forces or surface potential depending on the field gradients can be separated from the surface topography by dynamic SFM methods.
Small amplitude working in the repulsive regime.In this mode,the tip is oscillated in a range of1nm in the repulsive contact region,named force modulation mode(FMM). It provides an elastic or stiffness contrast of the sample.By measuring the response to the tip oscillation amplitudes,areas with different viscoelasticities can be detected. High amplitude mode in the intermittent regime.In this mode the SFM tip oscillates with high amplitudes(10±100nm)so that the tip propagates through large parts of the interaction potential in a single oscillation cycle,i.e.through attractive and repulsive regimes.Thus it is called intermittent contact mode(IC-mode)or tapping mode TM(Digi-
tal Instruments).Approaching the sample surface the oscillation amplitude and the fre-quency of the cantilever decreases with the average tip-sample distance.The feedback loop is controlled by keeping the amplitude or the frequency constant.In this mode,the contact time between the tip and the sample is reduced by two orders of magnitude as compared to the contact mode and is thus touching the surface only agentlyo.
High amplitude mode in the attractive regime .The high amplitude mode can also work in the effective attractive regime if the tip is set above the sample surface in a distance of 10±100nm (anon-contactomode).Another reliable way is to introduce an active feedback circuit instead of the standard feedback,Fig.5-4[29].In this design,the effective quality factor (Q-factor,Q =f /D f )of the oscillating system is increased by at least one order of magnitude.As a consequence the sensitivity is enhanced allowing to prevent the onset of tapping.This concept provides a means to control and enhance the size of the attractive interaction regime and thereby makes this operation mode more stable and usable in air and in liquids.This method is very use-ful for measuring soft materials which stick weakly to the substrate.
Magnetic force microscope (MFM)Long range forces such as magnetic or electro-static forces dominate the tip-sample interaction if the tip-sample separation exceeds 10nm.The long range magnetic or electrostatic forces are usually probed by using the a.c.-detection method.For magnetic force detection magnetic probing tips are neces-sary and it is realized by magnetic coating of the Si 3N 4tips which are commercially available.To achieve the separation of the topographic and the magnetic structures,the strength of the magnetic interaction can be modulated and measured by different methods [30].Alternatively,a modulated bias voltage can be applied.The resulting electrostatic forces cause an oscillation of the cantilever at the second harmonic.The amplitude of this oscillation can be used to drive the feedback loop [31].Simulta-neously,the d.c.force induced by the magnetic interaction can be detected.
140
Chi
detector
lock-in amplifier
PID-controller
x,y,z-scanner phase amplitude
Figure 5-4.Schematic diagram of the SFM with additional feedback circuit for active control of the sys-tem response function.The setup allows the effective quality factor of the dynamic system to be chan-ged by more than an order of magnitude (adapted from Anczykowski et al,[29]).
5.3.3Scanning near-field microscopy (SNOM)
In a transmission-type scanning near-field optical microscope (SNOM),as shown schematically in Fig.5-5,a tip of dimensions smaller than the wavelength of light serves as a light emitting antenna.It is excited by light from an external source by an optical path and a link which serves to transmit light from the optical path to the nanoscopic dimensions of the tip where optical components fail.Light emitted from the tip and transmitted through the object is converted by a detector into an electrical signal which is used for imaging.The probe is mounted on a piezoelectric scanner which scans the probe relatively to the object.In order to obtain a high resolution in the near field image,the distance between tip and object has to be kept smaller than the desired resolution.Therefore an auxiliary signal such as a SFM or STM signal is generally used to control the distance between tip and object.The tip and the link have specific near-field optical functions and therefore are the characteristic parts of a https://www.doczj.com/doc/ee10179871.html,ually,a glass fiber is used as the optical path and a conically tapered end coated with metal serves as a link.At the end of this link an aperture of a diameter in the range of 50to 100nm is formed at the tip which serves as a SNOM probe.One alternative to such an aperture probe is the tetrahedral tip which consists of the corner of a glass fragment which is coated with 50nm of gold.For a general description of SNOM see ref.[32].
The most important advantage of SNOM,named by some authors near-field scan-ning optical microscopy (NSOM),in comparison to other forms of optical microscopy and to other forms of SPM is the potential of a high lateral resolution below the dif-fraction limit in conjunction with optical spectroscopic contrast.
5.4Applications for characterizing nanophase materials
Applications of SPM methods for characterizing nanophased materials address the following questions:1)geometry of individual clusters and their size distribution on the surface of supporting substrates;2)binding and growth behavior of clusters on substrates;3)local physical properties;4)two-dimensional arrangement of clusters on substrates and 5)generation and fabrication of nanoclusters with SPM techniques.
Scanning Probe Microscopy of Nanoclusters
141
Figure 5-5.The characteristic components of a transmission-type scanning near-field microscope (adapted from U.Ch.Fischer,[32]).
142
Chi
5.4.1Individual nanoclusters
5.4.1.1Nanoclusters without protective coating
Shape and size distribution.A knowledge of the three-dimensional shape and size-distribution of supported clusters deposited on substrates could provide insight into the microscopic forces acting on surfaces and is important for a detailed understand-ing of many experimental results.Although research on free standing and supported clusters has clearly demonstrated the size-dependent structural and electronic features differing from bulk systems,it is not easy to measure the three-dimensional shape of supported cluster.SPMs offer alternative methods supplementing transmission elec-tron microscopy(TEM).With TEM intriguing questions arise sometimes whether clusters have their stable shapes in a high energy electron beam[33].
The early SPM studies on metal clusters were carried out with STM on highly ori-ented pyrolytic graphite(HOPG).Abraham et al[34]demonstrated the use of STM as a tool for the study of metal aggregates formed by metal vapor deposition.They were able to image isolated Ag clusters and the motion of clusters on the support. Baróet al[35]obtained constant current images in air of nanometer-sized Au clusters deposited on HOPG by using the multiple expansion cluster source(MECS),Fig.5-6. The width of the objects was determined by measuring the width at the half-maximum from the contour map.A mean size of12 with a standard deviation of2.7 was obtained,which was in good agreement with the13 diameter predicted by decelera-tion cell measurements on the cluster beam.
In these studies,the STM scans indicated substantial cluster mobility which hindered the reliable imaging and the following analysis.Suitable substrates have to be chosen for stronger binding of the clusters.Castro et al[36]extended the prelimin-ary experiments by exploring other substrates,such as Au and Pt.They inserted a piece of clean Au or Pt wire,1mm in diameter,into a gas torch flame.A molten sphere with a diameter of2mm was formed at the end of the wire,giving atomically flat facets.Stable STM images of large clusters(10±20nm in diameter)were obtained on both substrates.Small clusters with diameters<2nm were still difficult to image
due to the tip-cluster interaction.H?vel et al introduced a method to fix clusters on
Scanning Probe Microscopy of Nanoclusters143 HOPG[37].They produced nanometer-sized pits in the first layer of HOPG by sput-tering(with Ne ions)and following oxidation.On such a substrate small clusters,e.g. thermally evaporated Ag clusters with3.7nm in height,were stably imaged by UHV-STM.In addition,the pits acted as well-defined condensation centers,which led to a narrow size distribution and controllable cluster coverage.
Schaefer et al demonstrated that with dynamic mode SFM working in attractive re-gime clusters thermally evaporated on substrates such as HOPG,mica,Si and PbS could be readily imaged[38].Typical interaction forces between the tip and the sam-ple in this operating mode were in the range of10±10N.They found,however,that clusters with heights less than5nm and more than18nm were rarely seen with SFM, even though parallel TEM studies indicated that a detectable number of these clusters were present.It seemed likely that the small clusters were less bound to the surface and could be moved by the SFM tip even in this operating mode.The large clusters could be caused by a flattening of the clusters on the carbon film due to the surface force,or they could possibly be a result of a modification by the electron beam during TEM studies.Differences in the size distribution evaluated from STM and TEM measurements were also reported by other groups,e.g.by Granjaud et al[39].
Li et al[40]studied systematically the3D shape of preformed Au clusters with radii varying from1to6nm on flame annealed Au substrates by using STM.Based on the analysis of apparent cluster diameter D and cluster height H(D/H was larger than1), they found that the shape of the supported clusters resembled spherical caps rather than spheres.A characteristic radius of curvature between10and30nm was found, which was greater than and not correlated with the original free space radius of the clusters.The flatness of the supported clusters was considered to be attributed to plas-tic deformation induced by surface forces.Clusters whose radius of curvature was less than a critical value r*were subjected to internal stress in excess of their yield stress. On deposition this stress was relieved by cluster deformation when the cluster wetted the substrate.They believed that this behavior might be very common and might be useful for explaining other cluster experiments.Wurster et al indicated that the inter-pretation of the shape of clusters in the size range of5±50nm based on the SFM and FFM images had to be careful since the shape of the probing tip could strongly influ-ence imaging[41].They observed a clear difference in imaging hemispherical shaped indium clusters with an ordinary pyramidal tip(aspect ratio1:1)and a super tip on the top of the pyramid(aspect ratio>10:1).The hemispherical shape could only be ob-served with the super tip.
Sarid et al[42]demonstrated the possibility of applying STM on semiconductor clusters,e.g.BiI3deposited from colloidal suspensions on https://www.doczj.com/doc/ee10179871.html,ter Jing et al pre-sented STM images of Bi2S3clusters deposited on HOPG and gold surfaces[43].They observed disk-like structures independent of the nature of the substrate,as expected for clusters having layered symmetry.Again,larger clusters with a lateral dimension of10nm containing600atoms were reliably imaged,while smaller clusters were never stable enough to allow high quality images.
Growth of nanoclusters on substrates.Ganz et al extended the work of Baróet al to ultrahigh vacuum(UHV)[44].They determined adsorption sites of single metallic atoms(Ag and Au)and atomic spacing of small two-dimensional islands or rafts of metallic atoms on graphite.The islands contained ordered regions of roughly50atoms in rectangular lattices,incommensurate with the substrate lattice,https://www.doczj.com/doc/ee10179871.html,ter stud-ies have been carried out on different cluster and substrate combinations[45±51].
Humbert et al [48]indicated with STM images that in the Pd 2D clusters on HOPG the Pd atoms packed non-closed hexagonal with a lattice parameter of 4.26 which is definitively larger than the nearest neighbor distance of bulk Pd (2.74 ).Nie et al [50]proposed that the initial Pd atoms might occupy centers of the hexagonal units of HOPG and leave the six nearest-neighbor centers empty.They showed FFM high res-olution images giving the lattice distance of 2.8 (on mica substrate),which is com-parable to the bulk system.This means that during the growth of the Pd clusters,the lattice distance relaxed to that of the crystal.
Kern and coworkers reported recently the growth of nano-scale metallic islands by position selective electroless deposition (ELD)[52].ELD is an autocatalytic redox process in which metal ions are chemically reduced to metal at a surface in absence of any external current source.They used mixed amino-/alkanethiolate self-assembled monolayers (SAMs)on a gold electrode to provide special binding positions for palla-dium (Pd binds preferably to amino groups).The Pd 2+activated electrode was then used to grow Co islands.STM was used to observe in situ the growth of metal islands.It was revealed by STM that the density of the islands with a diameter between 1.5to 6nm for Pd and 1to 10nm for Co could be adjusted by changing the amine concen-tration in the aminothiolate/alkanethiolate SAMs.By using such a concept of metal deposition,and combining it with microcontact printing introduced by Whiteside and coworkers [53],it should be possible to fabricate diverse metal cluster arrays in desir-able patterns.
Mechanical properties of nanoclusters .Few works have addressed the mechanical properties of nanocluster.That may at least partially be related to the fact that the clusters can be easily swept away by applying contact SFM or FFM measurements [54].A systematic study of elastic properties of individual gold clusters preformed in the gas phase and deposited on diverse substrates (a -Al 2O 3,mica and HOPG)was reported by Schaefer et al with SFM [55].They scanned the sample with dynamic SFM first in order to position the tip on a single cluster.The elastic modulus of a clus-ter was then measured by nanoindentation described elsewhere [56]and compared
144
Chi
Figure 5-7.STM image of a monolayer Au island on graphite (a)and the computer model showing a rectangular lattice on the left and a honeycomb lattice on the right (Ganz et al,[44]).
with the bulk gold surface.The results were summarized as shown in Fig.5-8.For applied force loads less than 20nN,the annealed Au clusters showed an elastic modu-lus roughly 2/3of bulk Au,while the unannealed Au showed an elastic modulus roughly 1/6of bulk Au.The difference was likely due to the crystal defects in the unannealed cluster rather than to a size effect.5.4.1.2Passivated nanoclusters
Clusters stabilized by organic ligand shells (also named passivated nanocluster )have received increasing scientific interest in the recent years [57].The core of the cluster can be made of metals or semiconductors.The metallic clusters have a fixed number of atoms and thus a well defined size.They provide excellent model systems for monodispersed metal clusters,embedded in a dielectric matrix for the investiga-tion of physical properties related to nano-scale particles.The possible electronic ap-plications of these clusters as aquantum dotsoare discussed elsewhere [58].
The early works using STM to image passivated metallic clusters were done by van Kempen [59]and Becker et al [60].They applied STM,under atmospheric conditions,to gold and palladium clusters [Au 55(PPh 3)12Cl (a core of 55gold atoms stabilized by P(C 6H 5)3and Cl)and Pd 561(Phen)38+2O %200(561palladium atoms stabilized by phe-nanthrolin and O 2)],synthesized by G.Schmid [61].The clusters were deposited onto gold and graphite substrates from a droplet of aqueous suspension solutions.They found that the clusters could be easily dragged along with the scanning tip and even be picked up by the tip due to the very loose binding to the substrate.These effects hindered the imaging and could be minimized by increasing the distance between tip and substrate and decreasing the scanning speed to obtain stable imaging.On the other hand,once the clusters were picked up,they stayed at the outer end of the tip and thus provided a well defined tip,with a reproducible geometrical and electronic structure.They called the cluster-attached tip aknown tipoand the original PtIr tip cut with a pair of scissors aunknown tipo.They were able to measure single free-lying clusters with both kinds of tips.To distinguish single clusters with the STM,neverthe-less,became easier if the clusters were stacked densely.The STM images supported the idea that the clusters are more or less in a spherical form.The measured size dis-tribution of the clusters,evaluated from the measured heights of the clusters and their
Scanning Probe Microscopy of Nanoclusters
145
146
Chi
full width at half-maximum(FWHM)with a known tip was much smaller than that measured with an unknown tip.For all the cases,the width of the protrusion was a few times larger than the expected diameter of the clusters,while the height was signifi-cantly smaller.The deviation in width was obviously induced by the convolution of the tip,whereas the lack in the thickness was assumed to be induced from the defor-mation of the cluster,the deformation of the tip,or the fragmentation of the clusters on the substrates.
Reetz et al[62]determined the thickness of the protective surfactant layer on nano-sized palladium(Pd)clusters by a combination of STM and high resolution TEM. They used Pd clusters with an average diameter between2and4nanometers stabi-lized by tetraalkylammonium salts.The size of the ammonium ions was adjusted in the series+N(n±C4H9)4<+N(n±C8H17)4<+N(n±C18H37)4.STM images showed the size difference between a4.1nm Pd cluster stabilized with N(n±C8H17)4±Br and a2 nm Pd cluster stabilized with the same ammonium ion,Fig.5-9a and Fig.5-9b.The difference between the mean diameter(averaged over100particles)determined by STM(d STM)and TEM(d TEM)provided fairly detailed information of the interaction between the tetraalkyl ammonium ions and the metal clusters.The experimental results are summarized in Fig.5-9c and Fig.5-9d.In the case of different metal core and the same stabilizer,the geometric difference(d STM±d TEM)was nearly indepen-dent of the metal core diameter d TEM(Fig.5-9c);while in the case of the same metal core and different stabilizer,d STM±d TEM was directly dependent on the size of the ammonium ion(the length of the alkyl groups on+NR4),Fig.5-9d.The geometric difference(d STM±d TEM)correlated well with the monolayer thickness calculated with
a standard MM2force field.Thus,a monolayer protective coat was involved.The
Figure5-9.STM image of(a)a4.1nm Pd cluster stabilized by N(n±C8H17)4±Br and(b)a2nm Pd clus-ter stabilized by N(n±C8H17)4±Br.The influence of the metal core size on the STM image is summarized in(c)[stabilizer:N(n±C8H17)4±Br]and the influence of the stabilizer on the STM image is summarized in(d)(Reetz et al,[62]).
147
Scanning Probe Microscopy of Nanoclusters
results indicate that the combination of STM and high resolution TEM leads to valu-able information regarding the approximate geometric relation between the metal core and the stabilizing ligand shell.
5.4.2Structure of two-dimensionally arranged nanoclusters
5.4.2.1Monolayer of passivated metal clusters
The achievement of ordered arrays of metal dots is the essential step for developing nano-scale electronic devices[63].With this background,close-packed passivated metal clusters have been intensively studied by different research groups.Andres et al
[64]reported the preparation of ordered arrays of4nm gold clusters encapsulated by
a monolayer of alkyl thiol molecules by so called colloid self-assembly.The visualiza-tion of ordered cluster arrays was carried out with TEM.The colloid self-assembly was successfully applied to some other systems,see[65]as review.There are,however, rarely SPM studies on this kind of samples.This may result from the fact,that the solutions were normally dropped onto carbon film on copper grids and ready for TEM studies.
Two other methods to prepare2-dimensional arrangements of passivated nanoclus-ters were reported:two-step self-assembly(SA)-and Langmuir-Blodgett(LB)-tech-nique[66].The monolayer formation of ligand stabilized Au clusters or Au colloids on insulating and conductive substrates using two-step SA procedure was reported by several groups[67,68].The general idea is:generate a spacer layer carrying functional groups(e.g.±NH2)through self-assembly on the surface as the first step,and deposit the Au clusters with suitable groups in the ligand shell(e.g.±SO3H)as the second step.The surfaces were characterized by using SFM or STM.It turned out that this procedure lead to a high coverage of the surfaces(Fig.5-10a),but the packing was not as good(Fig.5-10b)as the colloid preparation.The advantage of this method is the
wide selectivity of the substrates.
Figure5-10.Monolayer of Au55cluster on gold substrate prepared by two-step self-assembly.The sur-face coverage is more than90%(a,SFM)and the clusters are densely packed(b,STM)(Chi et al,[68]).
148
Chi
Fendler et al applied the LB technique to prepare monolayers of various colloid nanoparticles[69].Later,Chi et al[70]and Bourgoin et al[71]reported the prep-aration of passivated cluster monolayers by using the same method and the SFM investigation on these monolayers.Water-insoluble metal clusters with hydrophobic ligand shells,e.g.Au55stabilized with phosphine(PPh3)Cl6or with oligo silsesquiox-ane derivative(T8±OSS),are not typical amphiphils used for LB preparation,but they are able to form stable monolayers at the air/water interface and can be transferred onto different solid substrates.One monolayer thickness was directly measured with SFM across the dipping line[70].
The transfer did not depend on the nature of the substrates.At a surface pressure of20mN/m,about1±5%uncovered areas or holes were observed by SFM[72].Some of the clusters were located on the top of the first monolayer.By transferring the monolayers at different surface pressures from the air/water interface,the surface cov-erage could be adjusted[70].WhileaSchmid clustersocould experience higher lateral surface pressures up to20mN/m,the dodecanethiol capped gold clusters(C12±Au) form multilayers at12mN/m[71].From SFM investigations,a pressure of8mN/m was found to be the optimum transfer pressure to minimize defects(either holes or multilayers)for this system.Such cluster layers were very fragile.In particular,they could be destroyed by STM and contact mode SFM.Bourgoin et al were successful to displace the dodecanethiol by2,5￠2-bis(acetylthio)-5,2￠,5￠,22-terthienyl(T3),by emerg-ing the LB monolayer of dodecanethiol capped Au clusters into T3solution overnight. After the displacement,the samples could be scanned stably with STM,Fig.5-11. STM images indicated that despite the relative polydispersity of the dodecanethiol Au particles,local hexagonal order was often observed in the film.Square order was also sometimes observed in very small areas.
T8-OSS-stabilized Au55clusters show increased stability in hydrocarbon solutions such as pentane and could be irradiated with an intensive electron beam in the elec-tron microscope without any aggregation or coalescence[72].They were,however, very loosely bound to the substrates with LB preparation.It was even difficult to image the monolayer of T8-OSS-stabilized Au55clusters with tapping mode.The dam-age to the sample is clearly seen in Fig.5-12a:the center part(100?200nm2)was
scanned only once in tapping mode.This effect strongly decreased the resolution since
Figure5-11.STM image taken on an interconnected arrays of gold particles prepared from a C12±Au monolayer deposited at8mN/m on epitaxial gold on mica(Bourgoin et al.[71]).
the damage became more pronounced by a smaller scanning area.This problem was solved by operating the SFM in the attractive regime using an active feedback circuit as mentioned in the experimental section.An SFM image of a monolayer without damage by operating SFM in this mode is shown in Fig.5-12b.The center part of the image (200?200nm 2)was scanned previously for more than one hour and no sample damage was observed.Finally,individual T 8±OSS-stabilized Au 55clusters could be visualized as shown in Fig.5-12c,which was only possible by operating high amplitude SFM in the attractive regime assisted by the active feedback controller.The measured cluster size is 5nm in diameter in good agreement with the expected value (4.2nm in diameter).The clusters formed short range ordered arrays,as indicated by black frames in Fig.5-12c.
5.4.2.2Nanosized metal/semiconductor dot arrays
Well ordered monolayers of colloid particles can be formed by drying the suspen-sion solutions on substrates and have been examined in detail [73].This approach offers another attractive method to prepare well ordered nano-dot arrays.
Scanning Probe Microscopy of Nanoclusters
149
Figure 5-12.(a)Monolayers of T 8±OSS-stabilized Au 55clusters undergo an easy deformation during scanning with SFM operated in the intermittent contact regime (middle part).(b)No deformation is observed when SFM is operated in the attractive regime assisted with the active feedback circuit.(c)With SFM operated in the attractive regime,individual Au 55±T 8±OSS clusters can be resolved (a and b:unpublished results from L.F.Chi,c:Schmid and Chi,[72]).
M?ller and coworkers[74]used amphiphilic diblock copolymers to form reverse micelles in a selective non-polar solvent,e.g.polystrene-block-poly(2-vinylpyridine) dissolved in toluene forms a core of poly(2-vinylpyridine)(P2VP)and a corona of polystyrene(PS).The polar block solubilizes metal salts such as HAuCl4,H2PtCl6, Pd(Ac)2and Ti(OR)4.Within the core chemical manipulations can be performed,e.g. confined salts can be reduced by UV light,electron beam or by suitable chemical reagents.Ultimately,singular metal or semiconductor particles of similar size are formed.The size of the particles is controlled by the micellar compartment between1 and15nm.Such a micellar solution can be cast on suitable substrates to form mono-micellar films.Finally,the polymer shell can be removed by plasma etching,while ordered arrays of single naked nanoparticles remain.
The formation of the nano-dot arrays was studied by SFM as well as TEM[75].The ordered structure could extend up to large macroscopic areas(3?3cm2).Figure5-13a shows a SFM image of a layer of PS(800)±b±P[2VP(HAuCl4)0.5(860)]after being trea-ted with an oxygen plasma operating at200W for20min.The polymer shell has been removed,exposing the single Au particles.The white dots display Au particles with12 nm in height and15nm in lateral dimension.By adjusting the polymer block,they succeeded in controlling the size of the naked nano-dots and the distance between them.Figure5-13b shows SFM images of organized Au cluster arrays loaded by PS(325)±b±P2VP(75)on mica.The size of the Au clusters is3nm in diameter with a periodicity of30nm.
Another promising technique to create ordered metallic nano-dot arrays is nano-sphere lithography[76]based on natural lithography[77].Hereby monolayers of closed packed monodisperse latex spheres with diameters from micrometer down to several ten nanometers are used as lithographic masks through which metals are deposited onto flat surfaces.The formation of metal dot arrays and the SFM observa-tion has been reported by several groups[78±81].The size of metallic dots prepared with this method can be reduced by annealing.For example,by using latex spheres 150
Chi
Figure5-13.SFM topography images of Au cluster arrays on mica substrates after the oxygen plasma treatment.The different interparticle distances are obtained by varying the lengths of the polymer blocks in the following way:(a)PS(800)±b±P[2VP(HAuCl4)0.5(860)],(b)PS(325)±b±P[2VP(HAuCl4)0.5(75)]and(c)PS(1700)±b±P[2VP(HAuCl4)0.1(450)].The size of each image corre-sponds to3m m 3m m(Spatz et al,[75]).
with a diameter of 220nm,one edge of the evaporated metallic triangular dots is about 70nm.After the flame annealing treatment,the dots change to a circular shape with a diameter of 20nm,while the packing of the dots remains unaffected [80].
By evaporating cobalt instead of gold,magnetic dot arrays were formed as shown in Fig.5-14a.[81].Application of magnetic force microscopy (MFM)revealed the sin-gle-domain state of the individual nanometer-sized cobalt dots which were magne-tized in an external field of 400Oe.The black-and white contrast in Fig.5-14b corre-sponds to the north and south poles of the Co-dots.Upon switching the magnetization direction,the black and white contrast above the Co-dots reversed (Fig.5-14c),which clearly proved the magnetic origin of the observed signal.5.4.2.3Surface of nanostructured solids
Nanostructured solids are prepared by compacting the clusters synthesized by gas condensation [82]or compacting the passivated clusters.The STM/SFM studies on such solid surfaces concentrate on the nanostructures and the grain boundaries after compacting.Houbertz et al resolved individual passiviated clusters with STM in com-pact pellets indicating only few clusters agglomerated [83].Wang and Ying et al imaged nanostructured palladium surfaces with STM and SFM [84,85],suggesting the equiaxed crystals of 10nm diameter joined together by grain boundaries.Migration of the grain boundaries was stimulated by STM (but not SFM),resulting in a preferential alignment of nanosized grains.I n another report of Ying et al [86]the nanosized tita-nium oxide (TiO 2±X )was found to adopt a prior preferential alignment by compact-ing.The TiO 2±X clusters with diameters of 10±20nm close packed in rows,as shown in Fig.5-15a,underwent structure change by heating.The individual clusters linked to-gether forming chain-like structures by heating the compact pellets.With further heat-ing the structures developed into smooth tubular structures,Fig.5-15b.The alignment phenomenon demonstrated step by step with the SFM could be of importance to mechanical and catalytic applications.
Scanning Probe Microscopy of Nanoclusters
151
Figure 5-14.(a)Topography SFM-image (1m m ?1m m)of a nanodot array consisting of cobalt particles.(b)MFM image showing the single domain state of the Co particles.The black and white contrast corre-sponds to the north and south poles of the Co-dots.An external magnetic field of 400Oe has been applied.(c)Corresponding MFM image of the same Co-dot-array upon reversal of the magnetization direction and the same magnitude (Winzer et al,[81]).
5.4.3SPM-based deposition and manipulation of metallic nanoclusters
Various SPM-based techniques have been successfully employed for nanofabrica-tion,e.g.atom manipulation [87],local oxidation [88],field-induced charge trapping [89].In this section,we will concentrate on the SPM-based deposition and manipula-tion of metallic nanoclusters.The general experimental approach is to apply a voltage pulse between the STM tip or metal coated SFM tip and the selected sample surfaces.Beyond a certain voltage threshold,nanosized clusters can be generated.Several mechanisms have been proposed for the cluster deposition,e.g.field evaporation of the tip material [90],point contact of the tip and the sample [91],and tip melting due to high electrical current [92].The advantage of SPM-based generation of nanoclus-ters lies in the subatomic accuracy of tip positioning which allows the deposition of clusters at the desired site.STM serves as well as the tool for the in situ characteriza-tion of the induced structures.
A number of pioneer works were carried out in the late 1980's.Staufer et al [93]created small hillocks of 35nm in diameter by locally melting glassy substrates.Silver et al [94]deposited metallic structures down to 20nm in size by decomposing organo-metallic gas with a https://www.doczj.com/doc/ee10179871.html,ter,McCord et al [95]reduced the size of metallic dots as small as 10nm by decomposing organometallic gases containing tungsten and gold.Schneir et al [96]and Li et al [97]demonstrated the possibility to deposit Au clusters on flat gold substrates with STM in air.Nanometer sized pits could be created as well with the same scanning tip.At that time,it was not possible to choose between mounts and pits forming under the tip.
A distinguished step to reliably deposit Au clusters on gold substrates was achieved by Mamin et al in 1990[98].They believed that the Au mounts deposited with the STM tip in the earlier experiments were induced by field evaporation as suggested by Gomer [90].To cause gold emission,they applied voltage pulse between the tip made of gold and the gold substrate while the tip was within the tunneling range.The pulses were sufficiently short (a few hundred nanoseconds or less)so that the feedback loop did not need to be disengaged during the pulsing.Figure 5-16a shows the gold mound
152
Chi
a)b)
Figure 5-15.(a)SFM image of nanocrystalline TiO 2±X compact.(b)SFM image of the same compact after being heated to 1000o C revealed the formation of tubular structures (adapted from Ying et al [86]).
《纳米材料》教学大纲 一、课程基本信息 课程编号：2 中文名称：纳米材料 英文名称：Nano-materials 适用专业：化学工程与工艺 课程类别：专业选修课 开课时间：第5学期 总学时：32 总学分：2 二、课程简介（字数控制在250以内） 《纳米材料》是化学工程与工艺专业的一门专业选修课，本课程系统地讲授各类纳米材料的概念、制备方法、结构和性能特征以及表征技术和方法，在此基础上，对其发展前景进行了展望。通过本课程的学习，引导大学生对纳米科学和技术进行认知与了解，帮助他们掌握纳米科技和纳米材料学的基本概念、基本原理、研究现状以及未来发展前景，从而启迪大学生的创新思维，拓宽其科学视野，培养他们对纳米科技的学习兴趣。 三、相关课程的衔接 与相关课程的前后续关系。 预修课程（编号）：高等数学B1（210102000913）、高等数学B2（210102000713）、物理化学A1（2）、物理化学A2（2），无机化学（A1）（2）、无机化学（A2）（2）。 并修课程（编号）：无特别要求 四、教学的目的、要求与方法 （一）教学目的 通过本课程的学习，引导大学生对纳米科学和技术进行认知与了解，帮助他们掌握纳米科技和纳米材料学的基本概念、基本原理、研究现状以及未来发展前景，从而启迪大学生的创新思维，拓宽其科学视野，培养他们对纳米科技的学习兴趣。 （二）教学要求 掌握纳米科技和纳米材料学的基本概念、基本原理、研究现状，对未来发展前景有一定的认识。
（三）教学方法 本课程遵循科学性、系统性、循序渐进、少而精和理论联系实际的教学原则，结合最新的研究成果着重讲述有关纳米材料的基本理论、理论知识的应用。本课程以课堂讲授教学为主，教学环节还包括学生课前预习、课后复习，习题，答疑、期末考试等。 五、教学内容（实验内容）及学时分配 （1学时） 第一章绪论（2学时） 1、教学内容 1.1纳米科技的基本内涵 1.2纳米科技的研究意义 1.3纳米材料的研究历史 1.4纳米材料的研究范畴 1.5纳米化的机遇与挑战 2、本章的重点和难点 本章重点是纳米科技与纳米材料的基本概念。 第二章纳米材料的基本效应（2学时） 1、教学内容 2.1 小尺寸效应 2.2 表面效应 2.3 量子尺寸效应 2.4宏观量子隧道效应 2.5 库仑堵塞与量子隧穿效应 2.6 介电限域效应 2.7 量子限域效应 2.8 应用实例 2、本章的重点和难点 重点：纳米材料的表面效应、小尺寸效应及量子尺寸效应。难点：宏观量子隧道效应。 第三章零维纳米结构单元（4学时） 1、教学内容 3.1 原子团簇
纳米材料的制备与表征方法摘录 作者姓名：彭家仁 单位：五邑大学广东江门 摘要:被誉为“21世纪最有前途的材料”的纳米材料同信息技术和生物技术一样已经成为21世纪社会经济发展的三大支柱之一和战略制高点。由于纳米材料的特殊结构以及所表现出来的特异效应和性能,使得纳米材料具有不同于常规材料的特殊用途。本文就纳米材料的结构特性和性能、应用及制备方法与表征进行了综述。旨在为纳米材料的应用及其制备提供理论指导。 关键词:纳米材料;结构特性;特异效应；应用;制备方法 Methods of Preparation and Characterization of nano-materials Kevin Peng (WUYI University Jiangmen Guangdong) Abstract:The nano-materials known as“the most promising material in the21st century”along with the information technology and the biotechnology has become one of the three pillars of the socio-economic development and the strategic high ground in the21st century.Because of the special structure of the nano-materials,as well as its specific effects and performance,thenano-materials have the special purposes other than the conventional materials. In this paper,we search for the structural properties,specific effect and the performance and the Synthesis and Characterization of nano-materials.The purpose is to provide theoretical guidance for the application and preparation of nano-materials. Keywords:nano-materials;structural properties;specific effect;applications;preparation methods 0前言 从人类认识世界的精度来看,人类的文明发展进程可以划分为模糊时代(工业革命之前)、毫米时代(工业革命到20世纪初)、微米和纳米时代(20世纪40年代开始至今)。自20世纪80年代初,德国科学家Gleiter提出“纳米晶体材料”的概念,随后采用人工制备首次获得纳米晶体,并对其各种物性进行系统的研究以来,纳米材料已引起世界各国科技界及产业界的广泛关注。纳米材料是指特征尺寸在纳米数量级(通常指1～100nm)的极细颗粒组成的固体材料。从广义上讲,纳米材料是指三维空间尺寸中至少有一维处于纳米量级的材料。通常分为零维材料(纳米微粒),一维材料(直径为纳米量级的纤维),二维材料(厚度为纳米量级的薄膜与多层膜),以及基于上述低维材料所构成的固体。从狭义上讲,则主要包括纳米微粒及由它构成的纳米固体(体材料与微粒膜)。纳米材料的研究是人类认识客观世界的新层次,是交叉学科跨世纪的战略科技领域。
纳米材料的测试与表征 目录 一、纳米材料分析的特点 二、纳米材料的成分分析 三、纳米材料的结构分析 四、纳米材料的形貌分析 一、纳米材料分析的特点 纳米材料具有许多优良的特性诸如高比表面、高电导、高硬度、高磁化率等； 纳米科学和技术是在纳米尺度上（0.1nm~100nm之间）研究物质（包括原子、分子）的特性和相互作用，并利用这些特性的多学科的高科技。 纳米科学大体包括纳米电子学、纳米机械学、纳米材料学、纳米生物学、纳米光学、纳米化学等领域。 纳米材料分析的意义 纳米技术与纳米材料属于高技术领域，许多研究人员及相关人员对纳米材料还不是很熟悉，尤其是对如何分析和表征纳米材料，获得纳米材料的一些特征信息。 主要从纳米材料的成分分析，形貌分析，粒度分析，结构分析以及表面界面分析等几个方面进行了检测分析。 通过纳米材料的研究案例来说明这些现代技术和分析方法在纳米材料表征上的具体应用。 二、纳米材料的成分分析 ●成分分析的重要性 ?纳米材料的光电声热磁等物理性能与组成纳米材料的化学成分和结构具有密切关 系 ?TiO2纳米光催化剂掺杂C、N ?纳米发光材料中的杂质种类和浓度还可能对发光器件的性能产生影响据报；如通过 在ZnS中掺杂不同的离子可调节在可见区域的各种颜色。 ?因此确定纳米材料的元素组成测定纳米材料中杂质种类和浓度是纳米材料分析的 重要内容之一。 ●成分分析类型和范围 ?纳米材料成分分析按照分析对象和要求可以分为微量样品分析和痕量成分分 析两种类型； ?纳米材料的成分分析方法按照分析的目的不同又分为体相元素成分分析、表面 成分分析和微区成分分析等方法； ?为达此目的纳米材料成分分析按照分析手段不同又分为光谱分析、质谱分析、 能谱分析 ●纳米材料成分分析种类 ?光谱分析:主要包括火焰和电热原子吸收光谱AAS，电感耦合等离子体原
纳米材料的制备以及表征 纳米科技作为21世纪的主导科学技术，将会给人类带来一场前所未有的新的工业革命。纳米科技使我们人类认识和改造物质世界的手段和能力延伸到原子和分子。纳米材料是目前材料科学研究的一个热点，纳米材料是纳米技术应用的基础。科学家们正致力于研究对纳米材料的组成、结构、形态、尺寸、排列等的控制，以制备符合各种预期功能的纳米材料。 低维纳米材料因其具有独特的物理化学特性以及在各个同领域的广泛应用 而受到国内外许多科研小组的广泛关注。钒氧化物纳米材料因为具有良好的催化性能、传感特性及电子传导特性而成为研究低维纳米材料物理化学现象的理想体系。尤其是对钒氧化合物纳米线、纳米带、纳米管的结构与性能的研究日益深入。另外，稀土正硼酸盐纳米材料因其独特的发光性能、电磁性能引起了广大科研小组的浓厚兴趣，是低维纳米材料领域研究的一个热点内容。 1.绪论 1.1纳米材料的发展概况 早在60年代，东京大学的久保良吾(Kubo)就提出了有名的“Kubo效应”， 认为金属超微粒子中的电子数较少，而不遵守Femri统计，并证实当结构单元变得比与其特性有关的临界长度还小时，其特性就会发生相应的变化。70年代末80年代初，随着干净的超微粒子的制取及研究，“Kubo效应”理论日趋完善， 为日后纳米技术理论研究打下了基础。人们对纳米颗粒的结构、形态和特性进行了比较系统的研究，描述金属微粒费密面附近电子能级状态的久保理论日趋完善，并且用量子尺寸效应成功地解释了超微粒子的某些特性[3]。最早使用纳米颗粒 制备三维块体试样的是德国萨尔兰大学教授H.Gletier，他于1984年用惰性气体蒸发、原位加压法制备了具有清洁表面的纳米晶Pd、cu、Fe等[4]，并从理论及性能上全面研究了相关材料的试样，提出了纳米晶材料的概念，成为纳米材料的创始者。1987年美国Argon实验室sigeel博士课题组用相同方法制备了纳米陶 瓷TIOZ多晶体。纳米技术在80年代末和90年代初得到了长足发展，并逐步成为一个纳米技术体系。1990年7月，第一届国际纳米科技会议在美国巴尔的摩 召开，标志着纳米科学技术的正式诞生;正式提出了纳米材料学、纳米生物学、
纳米材料的表征及其催化效果评价方式纳米材料的表征主要目的是确定纳米材料的一些物理化学特性如形貌、尺寸、粒径、等电点、化学组成、晶型结构、禁带宽度和吸光特性等。 纳米材料催化效果评价方式主要是在光照（紫外、可见光、红外光或者太阳光）条件下纳米材料对一些污染物质（甲基橙、罗丹明B、亚甲基蓝和Cr6+等）的降解或者对一些物质的转化（用于选择性的合成过程）。评价指标为污染物质的去除效率、物质的转化效率以及反应的一级动力学常数k的大小。
1 、结构表征 XRD，ED，FT-IR, Raman，DLS 2 、成份分析 AAS，ICP-AES，XPS，EDS 3 、形貌表征 TEM，SEM，AFM 4 、性质表征-光、电、磁、热、力等 … UV-Vis，PL，Photocurrent
1. TEM TEM为透射电子显微镜，分辨率为～，放大倍数为几万～百万倍，用于观察超微结构，即小于微米、光学显微镜下无法看清的结构。TEM是一种对纳米材料形貌、粒径和尺寸进行表征的常规仪器，一般纳米材料的文献中都会用到。 The morphologies of the samples were studied by a Shimadzu SSX-550 field-emission scanning electron microscopy (SEM) system, and a JEOL JEM-2010 transmission electron microscopy (TEM)[1]. 一般情况下，TEM还会装配High-Resolution TEM（高分辨率透射电子显微镜）、EDX（能量弥散X射线谱）和SAED（选区电子衍射）。High-Resolution TEM用于观察纳米材料的晶面参数，推断出纳米材料的晶型；EDX一般用于分析样品里面含有的元素，以及元素所占的比率；SAED用于实现晶体样品的形貌特征与晶体学性质的原位分析。
报告 课程名称纳米科学与技术专业班级电气1241 姓名张伟 学号32 电气与信息学院 和谐勤奋求是创新
纳米材料的测试与表征 摘要：介绍了纳米材料的特性及测试与表征。综合使用各种不同的分析和表征方法，可对纳米材料的结构和性能进行有效研究。 关键词：测试技术；表征方法；纳米材料 引言 纳米材料具有许多优良的物理及化学特性以及一系列新异的力、光、声、热、电、磁及催化特性，被广泛应用于国防、电子、化工、建材、医药、航空、能源、环境及日常生活用品中，具有重大的现实与潜在的高科技应用前景。纳米材料的化学组成及其结构是决定其性能和应用的关键因素，而要探讨纳米材料的结构与性能之间的关系，就必须对其在原子尺度和纳米尺度上进行表征。其重要的微观特征包括：晶粒尺寸及其分布和形貌、晶界及相界面的本质和形貌、晶体的完整性和晶间缺陷的性质、跨晶粒和跨晶界的成分分布、微晶及晶界中杂质的剖析等。如果是层状纳米结构，则要表征的重要特征还有：界面的厚度和凝聚力、跨面的成分分布、缺陷的性质等。总之，通过对纳米材料的结构特性的研究，可为解释材料结构与性能的关系提供实验依据。 纳米材料尺度的测量包括：纳米粒子的粒径、形貌、分散状况以及物相和晶体结构的测量；纳米线、纳米管的直径、长度以及端面结构的测量和纳米薄膜厚度、纳米尺度的多层膜的层厚度的测量等。适合纳米材料尺度测量与性能表征的仪器主要有：电子显微镜、场离子显微镜、扫描探测显微镜Χ光衍射仪和激光粒径仪等。 紫外和可见光谱是纳米材料谱学分析的基本手段，分为吸收光谱、发射光谱和荧光光谱。吸收光谱主要用于监测胶体纳米微粒形成过程；发射光谱主要用于对纳米半导体发光性质的表征，荧光光谱则主要用来对纳米材料特别是纳米发光材料的荧光性质进行表征。红外和喇曼光谱的强度分别依赖于振动分子的偶极矩变化和极化率的变化，因而，可用于揭示纳米材料中的空位、间隙原子、位错、晶界和相界等方面的信息。纳米材料中的晶界结构比较复杂，与材料的成分、键合类型、制备方法、成型条件以及热处理过程等因素均有密切的关系。喇曼频移与物质分子的转动和振动能级有关，不同的物质产生不同的喇曼频移。喇曼频率特征可提供有价值的结构信息，利用喇曼光谱可以对纳米材料进行分子结构、键态特征分析和定性鉴定等。喇曼光谱具有灵敏度高、不破坏样品、方便快速等优点，是研究纳米材料，特别是低维纳米材料的首选方法。 目前对纳米微观结构的分析表征手段主要有扫描探针显微技术，它包括扫描隧道电子显微镜、原子力显微镜、近场光学显微镜等。利用探针与样品的不同相互作用，在纳米级至原子级水平上研究物质表面的原子和分子的几何结构及与电子行为有关的物理、化学性质。例如用STM不仅可以观察到纳米材料表面的原子或电子结构，还可以观察表面存在的原子台阶、平台、坑、丘等结构缺陷。高分辨电子显微镜用来观察位错、孪晶、晶界、位错网络等缺陷，核磁共振技术可以用来研究氧缺位的分布、原子的配位情况、运动过程以及电子密度的变化；用核磁共振技术可以研究未成键电子数、悬挂键的类型、数量以及键的结构特征等。 测试技术的发展 纳米测试技术的研究大致分为三个方面：一是创造新的纳米测量技术，建立新理论、新方法；二是对现有纳米测量技术进行改造、升级、完善，使它们能适应纳米测量的需要；三是多种不同的纳米测量技术有机结合、取长补短，使之能适应纳米科学技术研究的需要。纳米测试技术是多种技术的综合，如何将测试技术与控制技术相融合，将探测、定位、测量、控制、信号处理等系统结合在一起构成一个大系统，开发、设计、制造出实用新型的纳米测量系统，是亟待解决的问题，也是今后发展的方向。随着纳米材料科学的发展和纳米制备技术的进步，将需要更新的测试技术和手段来表征、评价纳米粒子的粒径、形貌、分散和团聚
TiO 2纳米材料的制备与表征 医药化工学院 化学教育专业 学生：xxx 指导老师：xxx 1前言 纳米TiO 2在各个领域中的应用，如：制造氧敏元件、电子陶瓷材料、防晒剂、防紫外线透明塑料薄膜、农用塑料薄膜、防紫外纤维和抗菌纤维、抗菌涂料、抗菌釉面砖、效应颜料、光催化剂和催化剂载体、超双亲性玻璃等。这些材料在电子工业、涂料工业、轿车工业、建筑工业、纺织工业、食品包装、化妆品、环境保护、废水处理等领域中有着广泛的用途。 2实验部分 2.1 实验目的 了解TiO2纳米材料制备的方法；掌握用溶胶-凝胶法制备TiO2纳米材料的原理和过程；掌握纳米材料的标准手段和分析方法 2.2 实验原理 水解缩聚陈化涂层、成纤、成型干燥热处理金属醇盐 溶剂、水 抑制剂溶胶湿凝胶干凝胶 成品 Ti(OC4H9)4 + H2O ----> TiO2 + C4H9OH 实验装置图 2.3 实验仪器和试剂 2.3.1 主要仪器 常用常压化学合成仪器一套，电磁搅拌器，烘箱，马弗炉，粒度分布测定仪，比表面仪，差热-热重分析仪
2.3.2实验试剂 钛酸正丁酯，无水乙醇，乙酰丙酮，强酸 2.4 实验方法 2.4.1溶胶-凝胶法制备TiO 2 （1）水浴加热集热式恒温磁力搅拌器至65℃左右，安装三颈烧瓶装置、温度计和滴液漏斗，量取60ml的无水乙醇置于三颈烧瓶中。 （2）将30ml的钛酸四丁酯（Ti(OC4H9)4）装入滴液漏斗，自滴液漏斗缓慢滴加钛酸四丁酯（Ti(OC4H9)4）至装有无水乙醇三颈烧瓶中，保持反应温度为65℃左右，约0.5h滴加完毕。（3）滴加完毕后，将3ml乙酰丙酮装入入滴液漏斗，自滴液漏斗缓慢滴加乙酰丙酮至三颈烧瓶中，滴加完毕。再搅拌0.5小时。 （4）将1.1ml硝酸、9ml去离子水、32ml的无水乙醇预先混合，装入滴液漏斗，再缓慢加入到三颈烧瓶中，0.5小时滴加完毕，再搅拌3小时，得到二氧化钛溶胶，陈化12小时。（5）制备的二氧化钛溶胶至于60℃的真空干燥箱中干燥24小时，得到二氧化钛凝胶。（6）将制备的凝胶至于坩埚中，按照一定的升温曲线，600℃烧成保温2小时，得到二氧化钛粉末。 3.结果与讨论 mTiO2 =7.4g 颜色灰色 产率为 7.4/6.8=108.82% 4结束语 本实验溶胶-凝胶法制备TiO2通常以钛醇盐Ti(OR)4 为原料，合成工艺为：钛醇盐溶于溶剂中形成均相溶液，逐滴加入水后，钛醇盐发生水解反应，同时发生失水和失醇缩聚反应，生成1 nm 左右粒子并形成溶胶，经陈化，溶胶形成三维网络而成凝胶，凝胶在恒温箱中加热以去除残余水份和有机溶剂，得到干凝胶，经研磨后煅烧，除去吸附的羟基和烷基团以及物理吸附的有机溶剂和水，得到纳米TiO2 粉体。 通过两人一组实验，在实验过程中，培养了两人的合作精神。在指导老师的细心指导下，实验顺利进行，完成。在实验过程中，巩固了实验操作的基本技能，复习了课堂上的理论知识。实验过程中收获很大，感谢指导老师的悉心指导，同时也感谢同学们，因为有他们的合作，实验遇到的困难才一一得以解决，实验才顺利进行。 参考文献: 1) 北京师范大学, 等. 无机化学实验[M ]. 北京: 高等教育出版社, 1991.
物理在纳米材料测试表征中的应用 摘要：介绍了纳米材料的特性及一般的测试表征技术，主要从纳米材料的形貌分析，成分分析以及结构分析入手，介绍了扫描电子显微镜，透射电子显微镜，X 射线衍射，X射线荧光光谱分析，能谱分析等分析测试技术的工作原理及其在纳米粒子结构和性能分析上的应用和进展。 关键词：纳米材料；测试技术；表征方法 Abstract：The characterization and testing of nano-materials was described. Depend on the morphology, component and structure of nano-materials, the mechanism and applications of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray fluorescence spectroscopy, energy dispersive x-ray spectroscope (EDS) technology was presented. Further, the application and development of those technologies were described. Keyword: nano-materials; testing technology; characterization 0. 前言 分析科学是人类知识宝库中最重要、最活跃的领域之一，它不仅是研究的对象，而且又是观察和探索世界特别是微观世界的重要手段[ 1 ]。随着纳米材料科学技术的发展，要求改进和发展新分析方法、新分析技术和新概念，提高其灵敏度、准确度和可靠性，从中提取更多信息，提高测试质量、效率和经济性[ 2 ]。纳米科学和技术是在纳米尺度上（0. 1～100nm）研究物质（包括原子、分子）的特性及其相互作用, 并且对这些特性加以利用的多学科的高科技。纳米科技是未来高技的基础，而适合纳米科技研究的仪器分析方法是纳米科技中必不可少的实验手段。因此，纳米材料的分析和表征对纳米材料和纳米科技发展具有重要的意义和作用[ 3 ]。 1. 纳米材料的形貌分析 1.1 形貌分析的重要性
2.3.1 X 一射线衍射物相分析 粉末X 射线衍射法，除了用于对固体样品进行物相分析外，还可用来测定晶体 结构的晶胞参数、点阵型式及简单结构的原子坐标。X 射线衍射分析用于物相分析 的原理是:由各衍射峰的角度位置所确定的晶面间距d 以及它们的相对强度Ilh 是物 质的固有特征。而每种物质都有特定的晶胞尺寸和晶体结构，这些又都与衍射强 度和衍射角有着对应关系，因此，可以根据衍射数据来鉴别晶体结构。此外，依 据XRD 衍射图，利用Schercr 公式: θ λθβcos )2(L K = 式中p 为衍射峰的半高宽所对应的弧度值;K 为形态常数，可取0.94或0.89;为X 射线波长，当使用铜靶时，又1.54187 A; L 为粒度大小或一致衍射晶畴大小;e 为 布拉格衍射角。用衍射峰的半高宽FWHM 和位置(2a)可以计算纳米粒子的粒径， 由X 一射线衍射法测定的是粒子的晶粒度。样品的X 一射线衍射物相分析采用日本理 学D/max-rA 型X 射线粉末衍射仪，实验采用CuKa 1靶，石墨单色器，X 射线管电压 20 kV ，电流40 mA ，扫描速度0.01 0 (2θ) /4 s ，大角衍射扫描范围5 0-80 0，小角衍 射扫描范围0 0-5 0o 2.3.2热分析表征 热分析技术应用于固体催化剂方面的研究，主要是利用热分析跟踪氧化物制 备过程中的重量变化、热变化和状态变化。本论文采用的热分析技术是在氧化物 分析中常用的示差扫描热法(Differential Scanning Calorimetry, DSC)和热重法 ( Thermogravimetry, TG )，简称为DSC-TG 法。采用STA-449C 型综合热分析仪(德 国耐驰)进行热分析，N2保护器。升温速率为10 0C.1 min - . 2.3.3扫描隧道显微镜 扫描隧道显微镜有原子量级的高分辨率，其平行和垂直于表面方向的分辨率 分别为0.1 nm 和0.01nm ，即能够分辨出单个原子，因此可直接观察晶体表面的近原 子像;其次是能得到表面的三维图像，可用于测量具有周期性或不具备周期性的 表面结构。通过探针可以操纵和移动单个分子或原子，按照人们的意愿排布分子 和原子，以及实现对表面进行纳米尺度的微加工，同时，在测量样品表面形貌时， 可以得到表面的扫描隧道谱，用以研究表面电子结构。测试样品的制备:将所制 的纳米Fe203粉末分散在乙醇溶液中，超声分散30 min 得红色悬浊液，用滴管吸取 悬浊液滴在微栅膜上，干燥，在离子溅射仪上喷金处理。采用JSM-6700E 场发射扫 描电子显微镜旧本理学)，JSM-6700E 场发射扫描电子显微镜分析样品形貌和粒 径，加速电压为5.0 kV o 2.3.4透射电子显微镜 透射电镜可用于观测微粒的尺寸、形态、粒径大小、分布状况、粒径分布范 围等，并用统计平均方法计算粒径，一般的电镜观察的是产物粒子的颗粒度而不 是晶粒度。高分辨电子显微镜(HRTEM)可直接观察微晶结构，尤其是为界面原 子结构分析提供了有效手段，它可以观察到微小颗粒的固体外观，根据晶体形貌 和相应的衍射花样、高分辨像可以研究晶体的生长方向。测试样品的制备同SEM 样品。本研究采用 JEM-3010E 高分辨透射电子显微镜(日本理学)分析晶体结构， 加速电压为200 kV o 2.3.5 X 射线能量弥散谱仪 每一种元素都有它自己的特征X 射线，根据特征X 射线的波长和强度就能得
纳米材料AlO（OH）的制备与表征 刘琦媛吉大物理学院2011级光信六班32110635 摘要:利用超声水合合成法使电爆炸法制成的纳米Al粉和去离子水反应制备纳米纤维AlO（OH）粉末，然后用投射电镜观察其结构样貌，并用氮吸附法测定其BET比表面。 关键词：超声水合合成法，一维纳米纤维，AlO（OH），氮吸附法，BET比表面 1.引言 纳米材料，是科学界中正冉冉升起的一颗新星。自20世纪70年代初发现和应用纳米效应以来。人们对于它的研究，越发深入：贯穿物理、化学、生物、材料等多个层次。因为各种性质的特殊，纳米材料的作用越来越大。随着纳米技术的发展，它在人们生产、生活中的地位终将无可取代。 从广义上讲，纳米材料是指在三围空间尺寸中至少有一维处于纳米尺度范围或由它们作为基本单元构成的材料。如果按维数，纳米材料大致可分为量子点，量子线和量子阱。从狭义上讲，则只要包括纳米微粒及由它构成的纳米固体都可称为纳米材料。纳米材料尺寸进入纳米量级（1~100nm）时，其本身具有的量子尺寸效应、表面效应和宏观量子隧道效应因而展现出许多特有性质。在催化、滤光、光吸收、医药、磁介质及新材料方面有广阔的应用前景。
本实验研究的是一维纳米纤维AlO（OH）的制备与表征，这种纳米纤维材料纯度高，比表面积大，活性很高，吸附能力强且制备工艺简单，是很有发展前景的一种净水材料。 2. 实验 2.1实验试剂与仪器 试剂：1.电爆炸法制成的纳米铝粉 2.去离子水 仪器：1.电子天平 2.超声波清洗器 3.电热鼓风干燥箱 4.ZHP-100智能恒温震荡培养箱 5.透射电镜(TEM) 6.比表面及孔径分析仪(BET) 2.2纳米纤维的制备 本实验采用超声水合合成法制备一维纳米纤维AlO(OH)。 实验中使用的原料为电爆炸法所制成的纳米铝粉和去离子水。电爆炸法是利用高密度脉冲电流通过导体金属的瞬间，导体发生爆炸性破坏爆炸的产物——金属蒸汽在导体周围高速飞溅，在分散过程中爆炸产物被冷激而形成高弥散粉体。 实验过程：将0.8g纳米Al粉和200ml去离子水放入烧杯混合，放在超声波清洗器里进行反应，反应时间为120min，温度为80℃。 反应方程为： AlN+H2O=AlO(OH)+H2↑+NH3↑ 反应结束后关闭超声波清洗器，将烧杯取出放在温度为80℃的恒温水浴箱里6小时。之后过滤，将得到的物质放进电热鼓风干燥箱进行烘干。烘干条件为温度60℃，时长6小时。取出烘干物即得到纳米
纳米材料的表征与测试技术 作者：马翔（08级理学院材料化学系学生081132班） 摘要 虽然许多研究人员已经涉足纳米技术这个领域的工作，但还有很多研究人员以及相关产业的从业人员刘一纳米材料还不是很熟悉，尤其是如何分析和表征纳米材料，如何获得纳米材料的一此特征信息。该文对纳米材料的一此常用分析和表征技术做了概括。主要从纳米材料的成分分析、形貌分析、粒度分析、结构分析以及表面界面分析等几个方而进行了简要阐述。 关键词：纳米材料;表征;测试技术 1纳米材料的表征方法 纳米材料的表征主要包括: 1化学成分; 2纳米粒子的粒径、形貌、分散状况以及物相和晶体结构; 3纳米粒子的表面分析。 1. 1化学成分表征 化学成分是决定纳米粒子及其制品性能的最基本因素。常用的仪器分析法主要是利用各种化学成分的特征谱线，如采用X射线荧光分析和电子探针微区分析法可对纳米材料的整体及微区的化学组成进行测定。而且还可以与扫描电子显微镜SEM配合，使之既能利用探测从样品上发出的特征X 射线来进行元素分析，又可以利用二次电子、背散射电子、吸收电子信号等观察样品的形貌图像。即可以根据扫描图像边观察边分析成分，把样品的形貌和所对应微区的成分有机的联系起来，进一步揭示图像的本质。此外，还可以采用原子l发射光谱AES、原子吸收光谱AAS对纳米材料的化学成分进行定性、定量分析;采用X射线光电子能谱法XPS可分析纳米材料的表一面化学组成、原子价态、表面形貌、表面微细结构状态及表面能态分布等。 1.2纳米徽粒的衰面分析 (1)扫描探针显徽技术SPM 扫描探针显徽技术SPM以扫描隧道电子显微镜STM ,原子力显徽镜AFM、扫描力显微镜SFM 、弹道电子发射显徽镜BEEM、扫描近场光学显微镜SNOM等新型系列扫描探针显徽镜为主要实验技术，利用探针与样品的不同相互作用，在纳米级乃至原子级的水平 上研究物质表面的原子和分子的几何结构及与电子行为有关的物理、化学性质，在纳米尺度上研究物质的特性。 (2)谱分析法
实验名称：水热法制备纳米TiO2 水热法属于液相反应的范畴，是指在特定的密闭反应器中采用水溶液作为反应体系，通过对反应体系加热、加压而进行无机合成与材料处理的一种有效方法。在水热条件下可以使反应得以实现。在水热反应中，水既可以作为一种化学组分起反应并参与反应，又可以是溶剂和膨化促进剂，同时又是一种压力传递介质，通过加速渗透反应和控制其过程的物理化学因素，实现无机化合物的形成和改进。 水热法在合成无机纳米功能材料方面具有如下优势：明显降低反应温度（100-240℃）；能够以单一步骤完成产物的形成与晶化，流程简单；能够控制产物配比；制备单一相材料；成本相对较低；容易得到取向好、完美的晶体；在生长的晶体中，能均匀地掺杂；可调节晶体生成的环境气氛。 一．实验目的 1.了解水热法的基本概念及特点。 2.掌握高温高压下水热法合成纳米材料的方法和操作的注意事项。 3.熟悉XRD操作及纳米材料表征。 4.通过实验方案设计，提高分析问题和解决问题的能力。 二．实验原理 水热法的原理是：水热法制备粉体的化学反应过程是在流体参与的高压容器中进行，高温时，密封容器中有一定填充度的溶媒膨胀，充满整个容器，从而产生很高的压力。为使反应较快和较充分的进行，通常还需要在高压釜中加入各种矿化物。 水热法一般以氧化物或氢氧化物（新配置的凝胶）作为前驱物，他们在加热过程中溶解度随温度的升高而增加，最终导致溶液过饱和并逐步形成更稳定的氧化物新相。反应过程的驱动力是最后可溶的的前驱物或中间产物与稳定氧化物之间的溶解度差。 三．实验器材 实验仪器：10ml量筒；胶头滴管；50ml烧杯；高压反应釜；烘箱；恒温磁力搅拌器。 实验试剂：无水TiCl4；蒸馏水；无水乙醇。 四．实验过程 1.取10mL量筒, 50mL的烧杯洗净并彻底干燥。 2.取适量冰块放入烧杯中，并加入一定的蒸馏水形成20mL的冰水混合物，用恒温磁力搅拌器搅拌，速度适中。 ，缓慢滴加到冰水混合物中。 3.用量筒量取2mL的无水TiCl 4
材料的表征方法 2.3.1 X 一射线衍射物相分析 粉末X 射线衍射法，除了用于对固体样品进行物相分析外，还可用来测定晶体 结构的晶胞参数、点阵型式及简单结构的原子坐标。X 射线衍射分析用于物相分析 的原理是:由各衍射峰的角度位置所确定的晶面间距d 以及它们的相对强度Ilh 是物 质的固有特征。而每种物质都有特定的晶胞尺寸和晶体结构，这些又都与衍射强 度和衍射角有着对应关系，因此，可以根据衍射数据来鉴别晶体结构。此外，依 据XRD 衍射图，利用Schercr 公式: θ λθβc o s )2(L K = 式中p 为衍射峰的半高宽所对应的弧度值;K 为形态常数，可取0.94或0.89;为X 射线波长，当使用铜靶时，又1.54187 A; L 为粒度大小或一致衍射晶畴大小;e 为 布拉格衍射角。用衍射峰的半高宽FWHM 和位置(2a)可以计算纳米粒子的粒径， 由X 一射线衍射法测定的是粒子的晶粒度。样品的X 一射线衍射物相分析采用日本理 学D/max-rA 型X 射线粉末衍射仪，实验采用CuKa 1靶，石墨单色器，X 射线管电压 20 kV ，电流40 mA ，扫描速度0.01 0 (2θ) /4 s ，大角衍射扫描范围5 0-80 0，小角衍 射扫描范围0 0-5 0o 2.3.2热分析表征 热分析技术应用于固体催化剂方面的研究，主要是利用热分析跟踪氧化物制 备过程中的重量变化、热变化和状态变化。本论文采用的热分析技术是在氧化物 分析中常用的示差扫描热法(Differential Scanning Calorimetry, DSC)和热重法 ( Thermogravimetry, TG )，简称为DSC-TG 法。采用STA-449C 型综合热分析仪(德 国耐驰)进行热分析，N2保护器。升温速率为10 0C.1 min - . 2.3.3扫描隧道显微镜 扫描隧道显微镜有原子量级的高分辨率，其平行和垂直于表面方向的分辨率 分别为0.1 nm 和0.01nm ，即能够分辨出单个原子，因此可直接观察晶体表面的近原 子像;其次是能得到表面的三维图像，可用于测量具有周期性或不具备周期性的 表面结构。通过探针可以操纵和移动单个分子或原子，按照人们的意愿排布分子 和原子，以及实现对表面进行纳米尺度的微加工，同时，在测量样品表面形貌时， 可以得到表面的扫描隧道谱，用以研究表面电子结构。测试样品的制备:将所制 的纳米Fe203粉末分散在乙醇溶液中，超声分散30 min 得红色悬浊液，用滴管吸取 悬浊液滴在微栅膜上，干燥，在离子溅射仪上喷金处理。采用JSM-6700E 场发射扫 描电子显微镜旧本理学)，JSM-6700E 场发射扫描电子显微镜分析样品形貌和粒 径，加速电压为5.0 kV o 2.3.4透射电子显微镜 透射电镜可用于观测微粒的尺寸、形态、粒径大小、分布状况、粒径分布范 围等，并用统计平均方法计算粒径，一般的电镜观察的是产物粒子的颗粒度而不 是晶粒度。高分辨电子显微镜(HRTEM)可直接观察微晶结构，尤其是为界面原 子结构分析提供了有效手段，它可以观察到微小颗粒的固体外观，根据晶体形貌 和相应的衍射花样、高分辨像可以研究晶体的生长方向。测试样品的制备同SEM 样品。本研究采用 JEM-3010E 高分辨透射电子显微镜(日本理学)分析晶体结构， 加速电压为200 kV o
MXene的制备及其相关性能研究 1.1 MXene研究背景及现状 石墨烯是一种由碳原子以sp2杂化轨道组成的具有二维蜂窝状晶体结构的单原子层晶体，具有相当优异的力学、电子、热及磁学性能，而且被视为当今在纳米技术这个领域很有前景的材料[1]。石墨烯是二维晶体这一类的其中一种。二维晶体是指仅有单个或者多个原子厚度的二维材料，这种材料因为其绝对的二维结构而具备独有的特性与功能。石墨烯是最为典型的二维晶体结构，具有优异的性能，不过石墨烯却不是二维原子晶体材料的尽头，一些具有特殊性能并且包含其它元素的二维晶体成为当今的研究焦点。二维晶体材料可分为石墨烯基和类石墨烯这两大类材料。石墨烯基材料[2]是指包括石墨烯在内的二维原子晶体或化合物，例如单原子层的六方BN、MoS2、WS2等[3]。大部分的二维晶体材料是通过化学刻蚀或机械剥离等方法剥离层间结合力较弱(范德华力)的三维层状前驱物得到的，而剥离层间结合力较强的三维层状化合物似乎是不可能的。但是，2011 年Naguib和Barsoum等利用氢氟酸(HF)选择性刻蚀掉三维层状化合物Ti3AlC2中的Al原子层得到具有类石墨烯结构的二维原子晶体化Ti3C2材料，2012年他们采用同样的方法刻蚀若干与Ti3AlC2具有类似结构的陶瓷材料MAX相，成功的制备出了Ti2C、Ta4C3( Ti0.5Nb0.5)2C(V0.5Cr0.5)3C2、Ti3CN等相应的二维过渡金属碳化物或碳氮化物[4]。这种具有类石墨烯结构的新型二维晶体化合物被命名为MXene。其化学式为M n + 1X n，n =1、2、3，M为早期过渡金属元素，X为碳或氮元素[5]。MXene的母体材料MAX相是一类化学式为M n + 1AX n的三元层状化合物，其中M、X、n与上述一样，A为主族元素。目前已知MAX相大约有60多种，Ti3AlC2是其代表性化合物[6]。由于MAX相数量众多，且包含多种元素，所以通过刻蚀MAX相可以制备出大量具有特殊性能的MXene，这对于二维晶体材料的制 1.2 MXene的制备 制备MXene的前驱体是MAX相。MAX相是一类集陶瓷和金属的优良特性于一身的三元层状材料，既像陶瓷一样，具有高弹性模量、低密度、良好的热稳定性和抗氧化性能；又像金属一样，具备优良的导热和导电性能,以及较低的硬度，可以像金属和石墨一样进行机械加工,并在高温下具有良好的塑性，及自润滑性能。研究表明,MAX的晶体结构中，X原子填充于M原子形成的八面体空
20卷6期 结 构 化 学 （JIEGOU HUAXUE ） Vol.20, No.6 2001.11 Chinese J. Struct. Chem. 425~438 [综合评述] 纳米材料的概述、制备及其结构表征 蔡元霸① 梁玉仓 （结构化学国家重点实验室，中国科学院福建物质结构研究所, 福州350002） 纳米材料在电子、光学、化工、陶瓷、生物和医药等诸多方面的重要应用而引起人们的高度重视。本文从以下3个方面加以论述。 一、纳米材料的概述：从分子识别、分子自组装、吸附分子与基底的相互关系、分子操作与分子器件的构筑，并通过具体的例证加以阐述，包括在STM 操作下单分子反应；有机小分子在半导体表面的自指导生长；多肽-半导体表面特异性选择结合；生物分子/无机纳米组装体；光驱动多组分三维结构组装体；DNA 分子机器。 二、纳米材料的若干制备方法和结构表征方法：制备方法包括：物理的蒸发冷凝法，分子束外延法（MBE ），机械球磨法，扫描探针显微镜法（SPM ）。化学的气相沉淀法（VCD ），液相沉淀法，溶胶-凝胶法（Sol-gel ），L-B 膜法，自组装单分子层和表面图案化法，水热/溶剂热法，喷雾热解法，样板合成法或化学环境限制法及自组装法。 三、若干结构表征方法包括：X-射线法（XRD ），扩展X 射线精细结构吸收谱（EXAFS ），X-射线光电子能谱（XPS ），光谱法，扫描隧道显微镜/原子力显微镜（STM/AFM ）和有机质谱法（OMS ）。 关键词：纳米制备，自组装，结构表征， 纳米器件 2001-03-14收到； 2001-10-16接受 ①通讯联系人 1 纳米材料概述: 所谓纳米材料，指的是具有纳米量级（1~100 nm ）的晶态或非晶态超微粒构成的固体物质。纳米材料真正纳入材料科学殿堂应是德国科学家Gleiter 等 [1] 于1984年首用惰性 气体凝聚法成功地制备了铁纳米微粒，并以它作为结构单元制成纳米块体材料。由于纳米材料具有显然不同于体材料和单个分子的独特性能——表面效应、体积效应、量子尺寸效应和宏观隧道效应等及它在电子、光学、化工、陶瓷、生物和医药等诸多方面的重要应用而引起人们的高度重 视[2] 。 1988年美国科学家 Cram [3] 和法国科学 家 Lehn [4] 在诺贝尔领奖会上发表了演说，他 们分别以《分子的主体·客体和它们复合物的设计》和《超分子化学范围和展望——分子、超分子和分子器件》为题，论述了他们在超分子化学研究领域所取得成就和展望。1990年 Lehn [5] 又发表了《超分子化学展望——从分子识别走向分子信息处理和自组织作用》。他们指出生物体内反应、输运和调节的第一步就是分子识别。它定义为底物被给定受体选择并结合而形成超分子结构的过程。这是主/客体分子之间有选择、有目标的结合；是结构明确的分子间相互作用模式。这种结合还要求受体分子与所要键合的底物分子在立体空间结构和电荷特征上的互补性以及为了适合其功能上要求所必须遵循的刚性和柔性平衡原则。因为受体结构稳定性需要刚性分子结构，但识别过程中的变换、调控、协同及变构则需要一定的柔性。这对生物体系尤为重要。从分子识别引导
化学化工学院材料化学专业实验报告实验实验名称：纳米ZnO的制备及表征. 年级:2015级材料化学日期：2017/09/20 姓名：汪钰博学号：222015316210016 同组人:向泽灵 一、预习部分 1.1 氧化锌的结构 氧化锌（ZnO）晶体是纤锌矿结构，属六方晶系，为极性晶体。氧化锌晶体结构中，Zn原子按六方紧密堆积排列，每个Zn原子周围有4个氧原子，构成Zn-O4配位四面体结构，四面体的面与正极面C(00001)平行，四面体的顶角正对向负极面(0001)，晶格常数a=342pm, c=519pm,密度为5.6g/cm3，熔点为2070K,室温下的禁带宽度为3.37eV. 如图1-1、图1-2所示： 图1-1 ZnO晶体结构在C (00001)面的投影 图1-2 ZnO纤锌矿晶格图
2 氧化锌的性能和应用 纳米氧化锌(ZnO)粒径介于1- 100nm 之间, 由于粒子尺寸小, 比表面积大, 因而, 纳米ZnO 表现出许多特殊的性质如无毒、非迁移性、荧光性、压电性、能吸收和散射紫外线能力等, 利用其在光、电、磁、敏感等方面的奇妙性能可制造气体传感器、荧光体、变阻器、紫外线遮蔽材料、杀菌、图象记录材料、压电材料、压敏电阻、高效催化剂、磁性材料和塑料薄膜等。同时氧化锌材料还被广泛地应用于化工、信息、纺织、医药行业。纳米氧化锌的制备是所有研究的基础。合成纳米氧化锌的方法很多, 一般可分为固相法、气相法和液相法。本实验采用共沉淀和成核/生长隔离技术制备纳米氧化锌粉。 3 氧化锌纳米材料的制备原理 不同方法制备的ZnO晶形不同，如： 3.1 共沉淀和成核/生长隔离法 借助沉淀剂使目标离子从溶液中定量析出是材料制备领域液相法的重要技术。常规共沉淀制备是将盐溶液与碱溶液直接混合并通过搅拌的方式实现，由于混合不充分，反应界面小、存在浓度梯度、反应速度和扩散速度慢，先沉淀的粒子上形成新沉淀粒子，新旧粒子的同时存在，导致粒子尺寸分布极不均匀。使合成材料的粒子尺寸和均分散性能受到很大影响，其
纳米材料的粒度分析 1．1前言 1．粒度分析的概念 大部分固体材料均是由各种形状不同的颗粒构造而成，因此，细微颗粒材料的形状和大小对材料结构和性能具有重要的影响。尤其对于纳米材料，其颗粒大小和形状对材料的性能起着决定性的作用。因此，对纳米材料的颗粒大小、形状的表征和控制具有重要的意义。一般固体材料颗粒大小可以用颗粒粒度概念来描述。但由于颗粒形状的复杂性，一般很难直接用一个尺度来描述一个颗粒大小，因此，在粒度大小的描述过程中广泛采用等效粒度的概念。 对于不同原理的粒度分析仪器，所依据的测量原理不同，其颗粒特性也不相同，只能进行等效对比，不能进行横向直接对比。如沉降式粒度仪是依据颗粒的沉降速度进行等效对比，所测的立径为等效沉速径，即用与被测颗粒具有相同沉降速度的同质球形颗粒的直径来代表实际颗粒的大小。激光粒度仪则是利用颗粒对激光的衍射和散射特性作等效对比，所测出的等效粒径为等效散射粒径，即用与实际被测颗粒具有相同散射效果的球形颗粒的直径来代表这个颗粒的实际大小。当被测颗粒为球形时，其等效粒径就是它的实际直径。但由于粉体材料颗粒的形状不可能都是均匀球形的，有各种各样的结构，因此，在大多数情况下粒度分析仪所测的粒径是一种等效意义上的粒径，和实际的颗粒大小分布会有一定的差异，因此只具有相对比较的意义。等效粒径（D）和颗粒体积（V）的关系可以用表达式D=1.24V1/3表示。此外，各种不同粒度分析方法获得的粒径大小和分布数据也可能不能相互印证，不能进行绝对的横向比较。 由于粉体材料的颗粒大小分布较广，可以从纳米级到毫米级，因此在描述材料粒度大小时，可以把颗粒按大小分为纳米颗粒、超微颗粒、微粒、细粒、粗粒等种类。依据这些颗粒的种类可以采用相应的粒度分析方法和仪器。近年来，随着纳米科学和技术的迅速发展，纳米材料的颗粒分布以及颗粒大小已经成为纳米材料表征的重要指标之一，在普通的材料粒度分析中，其研究的颗粒大小一般在100nm~1ｕm尺寸范围。面对纳米材料研究，其最关注的尺度范围。 在纳米材料分析和研究中，经常遇到的纳米颗粒通常是指颗粒尺寸为纳米量级（1~100nm）的超细微粒。由于该类材料的颗粒尺寸为纳米量级，本身具有小尺寸效应、量子尺寸效应、表面效应和宏观量子隧道效应，因此具有许多常规材料所不具备的特性，在催化、非线性光学、磁性材料、医药及新材料等方面具有广阔的应用前景。因此纳米材料的粒度大小、分布、在介质中的分散性能以及二次粒子的聚集形态等纳米材料的性能具有重要影响，所以，纳米材料的粒度分析是纳米材料研究的一个重要方面。同样由于纳米材料的特性和重要性，促进了粒度分析和表征的方法和技术的发展，纳米材料的粒度分析已经发展成为现代粒度分析的一个重要领域。 目前，对纳米材料进行粒度分析的方法和仪器种类很多，但由于各种分析方法和仪器的设计对被分析体系有一定的针对性，采用的分析原理和方法各异，因此，选择合适的分析方法和分析仪器十分重要。又因为各种粒度分析方法的物理基础不同，同一样品用不同的测量方法得到的粒径的物理意义甚至粒径大小也不同。此外，不同的粒度分析方法的使用范围也不同。若对分析仪器及被测体系没有准确的了解与把握，分子所得到的结果往往于实际结果有较大差异，不具有科学性和代表性。因此，根据被测对象、测量准确度和测量精度等选择的测量方法是十分重要和必要的。